Field of the Invention
The present invention relates to an optical apparatus, and particularly to an optical apparatus that controls a blur correcting lens based on an output from a detector configured to detect the position of the blur correcting lens through a magnetic component.
Description of the Related Art
An object image in an image captured by an image pickup apparatus such as a digital camera may suffer blurs or so-called hand blurs, for example, when hands of a user holding the camera body shake in the image pickup. For this reason, the digital camera can serve to correct any blurs in the object image in the image caused by the shakes applied to the camera body. A conventional blur correcting means is optical image blur correcting processing that cancels any image blurs.
In the optical image blur correcting processing, an angular velocity sensor initially detects the vibration applied to the camera body. Then, a blur correcting lens provided in an image-pickup optical system that forms an object image is moved based on the detection result to shift the optical axis of this image-pickup optical system. As a result, an image formed on a light-receiving surface of an image sensor moves, and the image blur is corrected.
One known method of detecting the position of the blur correcting lens uses a magnet attached to a mobile member and a magnetic sensor such as a Hall sensor. It is conventional to use a voice coil motor (hereinafter, referred to as a VCM) to drive the mobile member. The VCM is also driven by a magnetic field produced by a magnet and a coil. Therefore, when the Hall sensor and the VCM are disposed close to each other, a Hall element detects not only the magnetism produced by the magnet but also the magnetism produced by the coil of the VCM, and thus the position of the mobile member cannot be correctly detected. One conventional solution is to mechanically arrange the Hall sensor and the coil far from each other, but leads to increase in the size and cost of the image pickup apparatus.
Japanese Patent Laid-Open No. (“JP”) 2010-231043 proposes a method of controlling driving of a mobile member using a signal after a magnetic component canceler configured to cancel induced magnetism produced by a coil cancels the induced magnetism.
According to the method disclosed in JP 2010-231043, the magnetic component canceler is, for example, a secondary lowpass filter that handles influence of the induced magnetism on the Hall element. The magnetic component canceler works when there are no characteristic scattering and changes of the induced magnetism, but when an actual characteristic differs from a supposed induced magnetism characteristic due to scattering, the influence of the induced magnetism cannot be completely removed or may be excessively corrected. In an open-loop Bode plot illustrating a driving characteristic of the mobile member, a gain characteristic, which has lowered in a frequency band due to the influence of the induced magnetism, becomes high after the induced magnetism is cancelled, thereby adversely narrowing a gain margin in control. Moreover, driving noises at high frequency are recoded through a microphone of the image pickup apparatus.